Antenatal Diagnosis of Placental Attachment Disorders

Background: Morbidly adherent placenta is a spectrum of conditions characterized by an abnormal adherence of the placenta to the implantation site. Three major variants of adherent placentation can be recognized according to the degree of trophoblastic invasion through the myometrium and the uterine serosa: placenta accreta, placenta increta and placenta percreta. All varieties of invasive placentation are associated with a significant increase in maternal morbidity.Placenta previa and previous uterine surgery represent the major risk factors for invasive placentation. Prenatal diagnosis of invasive placentation is associated with a reduced risk of maternal complications such as peripartum blood loss, need for transfusions and rate of hysterectomy, as it allows a preplanned treatment of the condition, however the performance of antenatal ultrasound and of different sonographic signs is not consistent across published studies because of limited sample size, retrospective design, variability of inclusion criteria and definition of invasive placentation.

Objectives: The aim of this study is to systematically assess the performance of ultrasound in the prenatal diagnosis of placenta accreta and its variants and to evaluate the role of the different specific ultrasound signs in predicting disorders of invasive placentation. The sonographic signs assessed in this study were: (1) vascular lacunae within the placenta, (2) loss of normal hypoechoic retroplacental zone, (3) interruption of the bladder line and/or focal exophytic masses extending into the bladder space, considered together and labeled as 'abnormalities of the uterus - bladder interface.

Design:prospective, multicenter, observational study of pregnant women with placenta previa.

Methods: The investigators hypothesized that ultrasound has a sensitivity of at least 80% and a specificity of at least 97%, with 10% confidence intervals, for antenatal diagnosis of invasive placentation.The investigators would require 2048 women with placenta previa, of whom approximately 61 (3%) will have morbidly adherent placenta, to test the null hypothesis with a 0.05 risk of type I error (alpha). Supposing a 10% of women with incomplete follow up the investigators aim to enroll 2254 women in this study.

Diagnostic criteria that suggested placenta accreta, increta, or percreta included one or more of the following situations: (1) obliteration of the clear space, defined as the obliteration of any part of the echolucent area located between the uterus and placenta; (2) visualization of placental lacunae, defined as multiple linear, irregular vascular spaces within the placenta; and (3) interruption of the posterior bladder wall-uterine interface such that the usual continuous echolucent line appears instead as a series of dashes.